Sierra Leone Krio is the lingua franca and the de factonational language spoken throughout the West African nation of Sierra Leone. Krio is spoken by 97% of Sierra Leone's population and unites the different ethnic groups in the country, especially in their trade and social interaction with each other. Krio is the primary language of communication among Sierra Leoneans at home and abroad. The language is native to the Sierra Leone Creole people or Krios, (a community of about 300,000 descendants of freed slaves from the West Indies, United States and United Kingdom), and is spoken as a second language by millions of other Sierra Leoneans belonging to the country's indigenous tribes. English is Sierra Leone's official language, while Krio, despite its common use throughout the country, has no official status. Due to its similarity to English, it is often mistaken for English slang.

Krio is distinct from Pidgin English as it is a language in its own right, with fixed grammatical structures and rules. Krio also draws extensively from other European languages, namely Portuguese and French, e.g. the Krio word gentri/gentree, which means wealth or to acquire wealth, is derived from the Old French word "gentry," and the Krio word pickin, which means child, comes from the Portuguese word "pequeno."

The early roots of Krio are believed to go back to the Atlantic slave trade era in the 17th and 18th centuries when an English-based "pidgin" language (West African Pidgin English, also called Guinea Coast Creole English) arose to facilitate the coastal trade between Europeans and Africans. This early pidgin later became the lingua franca of regional trade among West Africans themselves and likely spread up the river systems to the African interior. After the founding of Freetown, this preexisting pidgin was incorporated into the speech of the various groups of freed slaves landed in Sierra Leone between 1787 and about 1855. The pidgin gradually evolved to become a stable language, the native language of descendants of the freed slaves (which are now a distinct ethnic and cultural group, the Creoles), and the lingua franca of Sierra Leone.[3]

Most ethnic and cultural Creoles live in and around Freetown, the capital of Sierra Leone, and their community accounts for only about 3% or 5.4% of Sierra Leone's total population (Freetown is the province where the return slaves from London and Nova Scotia settled).[4] However, because of their cultural influence in Sierra Leone — especially during the period of colonial rule — their language is used as the lingua franca among all the ethnic groups in Sierra Leone. Many Mendes, Temnes, and Limbas grow up in the interior of the country speaking both their native languages and Krio. Children born in Freetown to parents who are not ethnic Creoles grow up speaking Krio and only Krio as their mother tongue language.

The Creole people acted as traders and missionaries in other parts of West Africa during the 19th century, and as a result there are also Krio-speaking communities in The Gambia, Nigeria, Cameroon, and Equatorial Guinea.[5] As a result of Sierra Leone Creole migratory patterns, in the Gambia the Creole or Aku community speak a dialect that is very similar to Krio in Sierra Leone. A small number of liberated Africans returned to the land of their origins, such as the Saros of Nigeria who not only took their Western names with them but also Krio word like sabi which was installed into Nigerian Pidgin English.

During the period of colonial rule, Sierra Leoneans (particularly among the upper class) were discouraged from speaking Krio; but after independence from the United Kingdom in 1961, writers and educators began promoting its use. In the 1960s, Thomas Decker translated some of Shakespeare's plays into Krio, and composed original poetry in the language. In the 1980s the New Testament was translated into Krio.

While English is Sierra Leone's official language, the Ministry of Education began using Krio as the medium of instruction in some primary schools in Freetown in the 1990s. Radio stations now broadcast a wide variety of programs in Krio. Sierra Leonean politicians also routinely give public speeches in the language.

The New York City Public School system recently recognized Krio as a "home language" allowing children to be recognized as speaking Krio rather than other African languages.[citation needed]

There is no grammatical gender in Krio and nouns are marked as genitive by the suffix "-im" for the singular. The suffix "-dèm" is used to mark the plural, as well as the genitive plural e.g. "uman" ("woman").

Verbs do not conjugate according to person or number, but reflect their tense. Tense, aspect and mood are marked by one or more tense or aspect markers. The tense markers are 'bin' for the past tense and 'go' for the future, the absence of either shows the present tense. Aspect is shown by 'dòn' for perfective and 'de' for imperfective. Infinitive is marked by 'fòr' and conditional by a combination of 'bin' and 'go'. Tendency is marked by 'kin' and 'nòbar'. The verbal paradigm is as follows.

In addition, like many other Creoles, a question can be asked simply by intonation. E.g. Yu de go?: 'Are you going' vs yu de go: 'you are going.' Additionally the question particles 'ènti' and 'nòoso' can be used at the start or end of the phrase respectively.

There is no distinction between masculine and feminine in any person and, unlike Standard English, there is a 2nd person plural form. However, there are the hints of nominative, accusative and genitive cases.

Krio uses the Latin script but without Qq and Xx and with three additional letters from the African reference alphabet, Ɛɛ (open E), Ŋŋ (eng), and Ɔɔ (open O). Three tones can be distinguished in Krio and are sometimes marked with grave (à), acute (á), and circumflex (â) accents over the vowels for low, high, and falling tones respectively but these accents are not employed in normal usage. An alternative orthography with Latin letters only has been devised by Thomas Decker.

The complete alphabet with digraphs follows with Decker's orthography in parentheses:

In 2007, work was completed on an unsanctioned, dubbed Krio version of Franco Zeffirelli's 1977 film Jesus of Nazareth The dubs were recorded by a team of over 14 native Krio speakers, over a period of 9 months in the Lungi region of Sierra Leone. The film aired on ABC-TV and a limited run of 300 copies were produced, which were mostly sold in Lungi and Freetown.[6]

The first feature-length documentary entirely spoken in Krio is Boris Gerrets' film Shado’man 2014.[7] It was shot in Freetown at night with a group of homeless disabled people. The film premiered at the IDFA documentary festival[8] in Amsterdam and was seen in festivals around the world including FESPACO, the biannual Pan-African film festival in Ouagadougou.[9]